This invention relates to gas electrodes, particularly activated carbon electrodes in sheet form bonded on one side to a gas porous membrane and on the other side to an electrically conductive layer or screen. The active carbon is usually catalyzed and mixed or coated in some manner to limit the quantity of solution coming into contact with it. One side of the gas electrode is in contact with a gas which is absorbed by the electrode, electrochemically reacts within the electrode to form a non-gaseous component which then passes through the electrode into the solution which is in contact with the other side of the electrode.
As one example of the prior art see Kordesch et al, U.S. Pat. No. 3,553,029 (1971). Kordesch et al teach a three layer electrode. The wet proof layer is polytetrafluoroethylene. The platinum activated carbon layer contains a binder and is bonded to a collector. The carbon used is activated carbon having a narrow range of pore diameters. Often the relatively large pores fill with liquid, a condition known as flooding. Kordesch, U.S. Pat. No. 3,899,354 (1975), teaches a catalyst concentration for the activated carbon. Landi, U.S. Pat. No. 3,704,171 (1972) discloses that a catalytic electrode layer, having a major component of a thermoplastic having a melting point lower than the sintering temperature of the polytetrafluoroethylene minor component, is made porous by dissolving the thermoplastic resin after fibrillating the hot plastic mixture.
While the prior art electrodes were very interesting from a scientific point of view, each of them had one or more weaknesses. One of the primary weaknesses was their inability to withstand an upset. This occurs when an oxygen cathode loses its oxygen supply while under load. A second weakness of the prior art electrodes made from activated carbon and polytetrafluoroethylene has been their lack of tensile strength. A third and major problem has been flooding. Flooding occurs when the solution saturates the porous components of the electrode and gas can no longer diffuse into the electrode to react electrochemically. This reaction is severely restricted when the electrode is flooded.
The electrodes of the present invention are very good at withstanding upsets, are also very good at withstanding high stress conditions which would destroy prior art electrodes, are very good at resisting flooding, and do not require the addition of fillers to make them porous.
The reason for the improved performance of the present electrodes over the prior art, is believed to reside in the two carbon component of the present electrode. The porous and hydrophobic nature of the carbon black component allows the passage of gas but not of solution. The porous and hydrophilic nature of the active carbon allows liquid to come into contact with the high surface area carbon black where reaction can occur. It is believed that reaction occurs on the surface of both the carbon black and the activated carbon, because effective results can be obtained by catalyzing either carbon or both. The electrode also functions, but not as well, if neither carbon is catalyzed. There are also a large number of other advantages which can be enumerated if each electrode of the present invention is compared with each prior art electrode on a one to one basis.